This invention relates to accelerated polymerizable compositions comprising compounds containing moieties capable of free radical polymerization, organoboron compounds capable of forming free radical generating species capable of initiating free radical polymerization and adhesives based on such compositions. In another embodiment the invention relates to a method of polymerizing compounds containing moieties capable of free radical polymerization and to methods of bonding substrates using such compositions.
Low surface energy olefins such as polyethylene, polypropylene and polytetrafluroethylene have a variety of attractive properties in a variety of uses, such as toys, automobile parts, furniture applications and the like. Because of the low surface energy of these plastic materials, it is very difficult to find adhesive compositions that bond to these materials. The commercially available adhesives that are used for these plastics require time consuming or extensive pretreatment of the surface before the adhesive will bond to the surface. Such pretreatments include corona treatment, flame treatment, the application of primers, and the like. The requirement for extensive pretreatment of the surface results in significant limitations to the designers of automobile components, toys, furniture and the like.
A series of patents issued to Skoultchi, U.S. Pat. Nos. 5,106,928; 5,143,884; 5,286,821; 5,310,835 and 5,376,746 (all incorporated herein by reference) and to Zharov, et al., U.S. Pat. Nos. 5,539,070; 5,690,780; and 5,691,065 (all incorporated herein by reference) disclose polymerizable acrylic compositions which are particularly useful as adhesives wherein organoboron amine complexes are used to initiate cure. It is disclosed that these complexes are good for initiating polymerization of an adhesive that bonds to low surface energy substrates. Pocius in a series of patents, U.S. Pat. No. 5,616,796; U.S. Pat. No. 5,621,143; U.S. Pat. No. 5,681,910; U.S. Pat. No. 5,686,544; U.S. Pat. No. 5,718,977; and U.S. Pat. No. 5,795,657 (all incorporated herein by reference) disclose amine organoboron complexes with a variety of amines used to complex the organoboron such as polyoxyalkylene polyamines and polyamines which are the reaction product of diprimary amines and compound having at least two groups which react with a primary amine.
A series of patents by Sonnenschein et al. U.S. Pat. Nos. 6,806,330; 6,730,759; 6,706,831; 6,713,578; 6,713,579 and 6,710,145, disclose amine organoboron complexes wherein the organoboron is a trialkyl borane and the amine is selected from the group of amines having an amidine structural component; aliphatic heterocycles having at least one nitrogen in the heterocyclic ring; an alicyclic compound having bound to the ring a substituent having an amine moiety; primary amines which in addition have one or more hydrogen bond accepting groups wherein there are at least two carbon atoms, preferably at least three carbon atoms, between the primary amine and the hydrogen bond accepting group; and conjugated imines. These patent applications disclose polymerizable compositions containing the amine organoboron complexes one or more of monomers, oligomers or polymers having olefinic unsaturation which are capable of polymerization by free radical polymerization and that the polymerizable compositions can be used as adhesive, sealant, coating or ink compositions.
Some of the references discussed above disclose the use of phenolic compounds, such as hydroquinones to stabilize the compositions against undesired polymerization. See Pocius, U.S. Pat. No. 5,684,102 at column 18, lines 45-53; Pocius, U.S. Pat. No. 5,861,910 at column 13 lines 17 to 24. Jennes, U.S. Pat. No. 3,236,823 discloses the use of hydroquinones, phenathiazine or t-butyl pyrocatechol as stabilizers in alkylborane initiated acrylate systems. Many of the disclosed compositions polymerize more slowly than is desired for use in industrial processes. This results in processes which exhibit low productivity.
Therefore, there is a need for adhesive systems that are capable of bonding to low surface energy substrates, and initiator systems which facilitate such bonding. What are further needed are polymer compositions and adhesive systems which are thermally stable at, or near, ambient temperatures and which will undergo polymerization when the user desires. Also needed are adhesive compositions which are capable of bonding to low surface energy substrates, and bonding low surface energy substrates to other substrates, without the need for extensive or costly pretreatment. Further compositions that can be used in existing commercial equipment at mix ratios of 4:1 or less are needed. Compositions that have stability, strength and adhesion at elevated temperatures are also desired. Further needed are compositions which cure rapidly as many industrial processes require fast cycle times.